font-weight - CSS: Cascading Style Sheets 编辑

The font-weight CSS property sets the weight (or boldness) of the font. The weights available depend on the font-family that is currently set.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

Syntax

/* Keyword values */
font-weight: normal;
font-weight: bold;

/* Keyword values relative to the parent */
font-weight: lighter;
font-weight: bolder;

/* Numeric keyword values */
font-weight: 100;
font-weight: 200;
font-weight: 300;
font-weight: 400;// normal
font-weight: 500;
font-weight: 600;
font-weight: 700;// bold
font-weight: 800;
font-weight: 900;

/* Global values */
font-weight: inherit;
font-weight: initial;
font-weight: unset;

The font-weight property is specified using any one of the values listed below.

Values

normal

Normal font weight. Same as 400.

bold

Bold font weight. Same as 700.

lighter

One relative font weight lighter than the parent element. Note that only four font weights are considered for relative weight calculation; see the Meaning of relative weights section below.

bolder

One relative font weight heavier than the parent element. Note that only four font weights are considered for relative weight calculation; see the Meaning of relative weights section below.

<number>

A <number> value between 1 and 1000, inclusive. Higher numbers represent weights that are bolder than (or as bold as) lower numbers. Certain commonly used values correspond to common weight names, as described in the Common weight name mapping section below.

In earlier versions of the font-weight specification, the property accepts only keyword values and the numeric values 100, 200, 300, 400, 500, 600, 700, 800, and 900; non-variable fonts can only really make use of these set values, although fine-grained values (e.g. 451) will be translated to one of these values for non-variable fonts using the Fallback weights system.

CSS Fonts Level 4 extends the syntax to accept any number between 1 and 1000 and introduces Variable fonts, which can make use of this much finer-grained range of font weights.

Fallback weights

If the exact weight given is unavailable, then the following rule is used to determine the weight actually rendered:

• If the target weight given is between 400 and 500 inclusive:
  • Look for available weights between the target and 500, in ascending order.
  • If no match is found, look for available weights less than the target, in descending order.
  • If no match is found, look for available weights greater than 500, in ascending order.
• If a weight less than 400 is given, look for available weights less than the target, in descending order. If no match is found, look for available weights greater than the target, in ascending order.
• If a weight greater than 500 is given, look for available weights greater than the target, in ascending order. If no match is found, look for available weights less than the target, in descending order.

Meaning of relative weights

When lighter or bolder is specified, the below chart shows how the absolute font weight of the element is determined.

Note that when using relative weights, only four font weights are considered — thin (100), normal (400), bold (700), and heavy (900). If a font-family has more weights available, they are ignored for the purposes of relative weight calculation.

Inherited value	bolder	lighter
100	400	100
200	400	100
300	400	100
400	700	100
500	700	100
600	900	400
700	900	400
800	900	700
900	900	700

Common weight name mapping

The numerical values 100 to 900 roughly correspond to the following common weight names (see the OpenType specification):

Value	Common weight name
100	Thin (Hairline)
200	Extra Light (Ultra Light)
300	Light
400	Normal (Regular)
500	Medium
600	Semi Bold (Demi Bold)
700	Bold
800	Extra Bold (Ultra Bold)
900	Black (Heavy)
950	Extra Black (Ultra Black)

Variable fonts

Most fonts have a particular weight which corresponds to one of the numbers in Common weight name mapping. However some fonts, called variable fonts, can support a range of weights with a more or less fine granularity, and this can give the designer a much closer degree of control over the chosen weight.

For TrueType or OpenType variable fonts, the "wght" variation is used to implement varying widths.

For the example below to work, you'll need a browser that supports the CSS Fonts Level 4 syntax in which font-weight can be any number between 1 and 1000.

HTML

<header>
    <input type="range" id="weight" name="weight" min="1" max="1000" />
    <label for="weight">Weight</label>
</header>
<div class="container">
    <p class="sample">...it would not be wonderful to meet a Megalosaurus, forty feet long or so, waddling like an elephantine lizard up Holborn Hill.</p>
</div>

CSS

/*
Mutator Sans is created by LettError (https://github.com/LettError/mutatorSans)
and is used here under the terms of its license:
https://github.com/LettError/mutatorSans/blob/master/LICENSE
*/

@font-face {
  src: url('https://mdn.mozillademos.org/files/16011/MutatorSans.ttf');
  font-family:'MutatorSans';
  font-style: normal;
}

label {
  font: 1rem monospace;
  white-space: nowrap;
}

.container {
  max-height: 150px;
  overflow-y: auto;
}

.sample {
  text-transform: uppercase;
  font: 1.5rem 'MutatorSans', sans-serif;
}

html, body {
  max-height: 100vh;
  max-width: 100vw;
  overflow: hidden;
}

body {
  display: flex;
  flex-direction: column;
}

header {
  margin-bottom: 1.5rem;
}

.container {
  flex-grow: 1;
}

.container > p {
  margin-top: 0;
  margin-bottom: 0;
}

JavaScript

let weightLabel = document.querySelector('label[for="weight"]');
let weightInput = document.querySelector('#weight');
let sampleText = document.querySelector('.sample');

function update() {
  weightLabel.textContent = `font-weight: ${weightInput.value};`;
  sampleText.style.fontWeight = weightInput.value;
}

weightInput.addEventListener('input', update);

update();

Accessibility concerns

People experiencing low vision conditions may have difficulty reading text set with a font-weight value of 100 (Thin/Hairline) or 200 (Extra Light), especially if the font has a low contrast color ratio.

• MDN Understanding WCAG, Guideline 1.4 explanations
• Understanding Success Criterion 1.4.8 | W3C Understanding WCAG 2.0

Formal definition

Initial value	normal
Applies to	all elements. It also applies to ::first-letter and ::first-line.
Inherited	yes
Computed value	the keyword or the numerical value as specified, with bolder and lighter transformed to the real value
Animation type	a font weight

Formal syntax

<font-weight-absolute> | bolder | lighter
where 
<font-weight-absolute> = normal | bold | [1,1000]>

Examples

Setting font weights

HTML

<p>
  Alice was beginning to get very tired of sitting by her sister on the
  bank, and of having nothing to do: once or twice she had peeped into the
  book her sister was reading, but it had no pictures or conversations in
  it, "and what is the use of a book," thought Alice "without pictures or
  conversations?"
</p>

<div>I'm heavy<br/>
  <span>I'm lighter</span>
</div>

CSS

/* Set paragraph text to be bold. */
p {
  font-weight: bold;
}

/* Set div text to two steps heavier than
   normal but less than a standard bold. */
div {
 font-weight: 600;
}

/* Set span text to be one step lighter
   than its parent. */
span {
  font-weight: lighter;
}

Result

Specifications

Specification	Status	Comment
CSS Fonts Module Level 4 The definition of 'font-weight' in that specification.	Working Draft	Defines font-weight to accept any numbers between 1 and 1000.
CSS Fonts Module Level 3 The definition of 'font-weight' in that specification.	Recommendation	No change.
CSS Level 2 (Revision 1) The definition of 'font-weight' in that specification.	Recommendation	No change.
CSS Level 1 The definition of 'font-weight' in that specification.	Recommendation	Initial definition.

Browser compatibility

BCD tables only load in the browser

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

See Also

• font-style
• font-family
• Fundamental text and font styling